Optical recording/reproducing method, recording medium used for optical recording and reproduction, and optical recording/reproducing apparatus

ABSTRACT

High density data storage device has a support substrate and one or more different types of phosphors contained at each of plural regularly arranged microscopic regions of the support substrate. Each of the different types of phosphors has a fluorescence characteristic that may be faded by incident light having a different predetermined wavelength. The use of near-field light facilitates a reduction in size of the space required for each data bit. By providing a plurality of different types of phosphors at each of the microscopic regions, the amount of information storable at each bit space is rendered multi-valued to enable higher density recording.

CROSS-REFERENCE TO RELATED PCT APPLICATION

This application is a U.S. National stage application of copendingInternational Application Ser. No. PCT/JP99/03637, filed on Jul. 6, 1999claiming a priority date of Jul. 7, 1998, and published in a non-Englishlanguage.

TECHNICAL FIELD

This invention relates to high density optical memories and, moreparticularly, to an optical recording/reproducing method utilizingnear-field light and recording medium fluorescent light, an opticalrecording/reproducing recording medium and an opticalrecording/reproducing apparatus.

BACKGROUND OF THE INVENTION

In recent years, in order to make [the] optical memories with higherdensity, there has been a shift in recording/reproducing methods fromcompact disks (CD) to digital video disks (DVD). For example, the CD inits surface is recorded with pits as concave/convex structures having asize of nearly a wavelength of laser light to be used upon reproducingand a depth of approximately a quarter of the wavelength. Forreproducing the information, interference of light is utilized, When alaser light spot is illuminated to the pit, because the pit depth isalmost a quarter wavelength, the difference in optical path between thereflection light reflected upon a pit bottom and the reflection light ona surface outside the pit is given a half of the wavelength of theilluminated laser light. Thus, the reflection light available is weak ascompared to the case of illuminating a laser light spot to the surfaceoutside the pit. In this manner, the presence or absence of a pit isdetermined by detecting an intensity of reflection light, thusreproducing information recorded on the CD. Although DVDrecording/reproducing is conducted by illuminating a laser light spot toa recording medium, the pit size can be made smaller than the CD byshortening a laser wavelength to be used thus enabling higher densityrecording/reproducing.

Meanwhile, there is known a near-field optical microscope for observinga microscopic surface texture of a sample by using a probe having amicroscopic aperture with a diameter of an illumination light wavelengthor smaller, e.g. approximately {fraction (1/10)}th of the wavelength,and through utilizing a near field (evanescent field). In thisnear-field optical microscope, the probe microscopic aperture and thesample surface are approached in distance to nearly the diameter of theprobe microscopic aperture so that a near field caused on the samplesurface due to illumination of propagation light from a sample backsideis detected by the probe. In this case, the near field caused on thesample surface involves an intensity and phase reflecting a samplesurface microscopic texture. This near field is scattered through theprobe microscopic aperture and extracted as propagation light, andreceived by a photodetector, thereby achieving a resolution unrealizedin the conventional optical microscope.

Consequently, the utilization of the near-field optical microscopetechnology as stated above makes possible recording/reproducingexceeding the recording density on the conventional informationrecording medium such as a CD or a DVD.

For high density recording/reproducing, there is a reduction of bit sizeand multi-valued bit information. It is possible for the DVD to conductrecording/reproducing with higher density than the CD by shortening theillumination light wavelength and thereby reducing the bit size.However, because of using means to reduce a spot diameter through alens, the illumination light spot diameter onto the recording mediumcannot be reduced to a half of the wavelength or smaller due to a lightdiffraction limit. Due to this, if the bit size becomes a halfwavelength of illumination light or smaller, it is impossible for theconventional optical system to record/reproduce information.Consequently, for recording/reproducing with higher density than theDVD, there is a need for shortening a wavelength to be used. Also, theCD and DVD obtain information only of 0, 1 from each bit without beingmulti-valued.

Meanwhile, if utilizing a near field that can reduce the spot diameterto a half of an illumination wavelength or smaller exceeding the lightdiffraction limit, high density recording/reproducing is feasible due toreducing the bit size. However, there has been no proposal to render theinformation from each bit multi-valued in order to provide higherdensity. Therefore, it is an object of the present invention to reducethe bit size by using a near field and at the same-time to provide ascheme for recording/reproducing multi-valued information for each bit,in order to realize high density recording/reproducing. Also, anotherobject is to obtain a recording medium and apparatus forrecording/reproducing.

DISCLOSURE OF THE INVENTION

In order to achieve the above objects, an optical recording methodaccording to the present invention illuminates a near-field light onto arecording medium having at least one or more types of phosphors, to fadefluorescence of a particular phosphor in a microscopic region on therecording medium. The use of near-field light can reduce the size of onerecording bit as compared to the conventional optical system using alens. Also, although the conventional method was recording of binaryvalues of 0, 1 for one recording bit, among a plurality of kinds ofphosphors, fluorescence of a particular phosphor only fades to recordthe presence or absence of fluorescence, rendering the informationamount on one recording bit multi-valued. From these, higher densityrecording than the conventional method is feasible.

Also, in an optical recording method according to the invention anear-field light having a corresponding wavelength to a particularphosphor is illuminated onto a recording medium having at least one ormore types of phosphors, to fade fluorescence of the particular phosphorin a microscopic region on the recording medium. The use of near-fieldlight can reduce the size of one recording bit as compared to theconventional optical system using a lens. Where fading fluorescence ofone kind of a particular phosphor, the fluorescence is faded byilluminating a light having a corresponding wavelength onto thisphosphor. At this time, fluorescence of other phosphors does not fade.Also, where fading fluorescence of a plurality of kinds of phosphors, acorresponding wavelength of light to each phosphor is illuminatedseparately or simultaneously, thereby fading fluorescence of them. Atthis time, fluorescence of the phosphor not corresponding to thewavelength dose not fade. In this manner, arbitrary phosphors arechanged in fluorescence whereby recording to one bit can be renderedmulti-valued. From this, higher density recording than the conventionalmethod is feasible.

Also, in an optical recording method according to the invention anear-field light is illuminated onto a recording medium having at leastone or more types of phosphors and the near-field light is changed inlight amount, to fade fluorescence of the particular phosphor in amicroscopic region on the recording medium. The use of near-field lightcan reduce the size of one recording bit as compared to the conventionaloptical system using a lens.

Also, fluorescence is faded in the order of fluorescence readier to bephotooxidized due to an illumination amount of near field light among aplurality of kinds of phosphors contained in a thin film, whereby theinformation amount of one recording bit can be rendered multi-valued.Also, where two kinds of phosphors are the same in light wavelength forfading fluorescence, it is impossible to vary the wavelength to fadefluorescence of either one of them. However, because the method ofchanging the illumination amount is not dependent upon the wavelength,one of the phosphors can be faded in fluorescence even where usingphosphors the same in light wavelength to fade fluorescence. From these,higher density recording is feasible than in the conventional.

Also, in an optical reproducing method according to the invention anear-field light is illuminated onto a recording medium having at leastone or more types of phosphors and recorded with data microscopically bythe presence or absence of fluorescence on a particular one of thephosphors, to specify a fluorescent one of the phosphors from a spectrumobtained. By detecting from a spectrum the presence or absence offluorescence on each phosphor contained in a recorded bit, it becomesfeasible to reproduce multi-valued information recorded on a microscopicbit.

Also, in a recording medium according to the invention a thin filmcontaining at least one or more types of phosphors is formed on asubstrate. By doing so, a recording medium for opticalrecording/reproducing is obtained which is increased in density byrendering information recording/reproducing multi-valued.

Also, in a recording medium according to the invention thin films eachhaving only one type of phosphor are formed on a substrate depending onthe kind of phosphor. Because each kind of phosphor is isolated, energytransfer between different phosphors is suppressed so that fluorescentlight can be obtained with efficiency. By doing so, a recording mediumfor optical recording/reproducing is obtained which is increased indensity by rendering information recording/reproducing multi-valued.

Also, a recording medium according to the invention forms an insulationfilm between the thin films formed. This causes energy transfer onlybetween the phosphors to thereby increase excitation efficiency,increasing fluorescent efficiency, obtaining intense fluorescent lightand improving the S/N ratio during reproduction. By doing so, arecording medium for optical recording/reproducing [could be] obtainedwhich is increased in density by rendering informationrecording/reproducing multi-valued.

Also, a recording medium according to the invention has on the substratea metal film on a side formed with the thin films. By doing so, theexcitation light illuminated to a recording medium surface transmitsthrough each thin film, and is thereafter reflected on the metal filmand again, illuminates the thin film, improving excitation efficiencyand increasing fluorescent intensity. By doing so, a recording mediumfor optical recording/reproducing is obtained which is increased indensity by rendering information recording/reproducing multi-valued.

Also, an optical recording apparatus according to the present inventioncomprises: a recording medium having phosphors, a head for producing anear-field light, an adjusting mechanism for adjusting a wavelengthand/or a light intensity of the near-field light, and an approachingmechanism to cause the recording medium and fluorescence of the head toapproach. Due to this, a near-field light can be illuminated only to amicroscopic region on the recording medium, and fluorescence of thephosphors contained in the microscopic region of the recording mediumcan be faded in fluorescence by using a near-field light, obtaining ahigh density optical recording apparatus.

Also, an optical reproducing apparatus according to the inventioncomprises a recording medium having phosphors, a head for producing anear-field light to excite the phosphors, a mechanism for specifying afluorescent one of the phosphors from a spectrum of the recordingmedium, and an approaching mechanism to cause the recording medium andthe head to approach. Due to this, a high density optical reproducingapparatus is obtained which illuminates a near-field light to arecording medium having at least one kind or more of phosphors andmicroscopically faded in particular fluorescence of the phosphors tospecify a fluorescent phosphor from an obtained spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a recording method according toEmbodiment 1 of the present invention.

FIG. 2 is a schematic view showing a reproducing method according toEmbodiment 2 of the present invention.

FIG. 3 is a schematic view showing an apparatus for performing recordingand reproducing according to Embodiment 3 of the present invention.

FIG. 4 is a schematic view showing a recording medium according toEmbodiment 3 of the present invention.

FIG. 5 is a schematic view showing a recording medium according toEmbodiment 4 of the present invention.

FIG. 6 is a schematic view showing a recording medium according toEmbodiment 5 of the present invention.

FIG. 7 is a schematic view showing a recording medium according toEmbodiment 6 of the present invention.

FIG. 8 is a schematic view showing a recording medium according toEmbodiment 7 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, in order to realize high density opticalrecording/reproducing concerning the present invention, explanationswill be made based on the drawings in detail of embodiments of arecording/reproducing method capable of reducing recording bit sizeusing near-field light and obtaining multi-valued information from eachbit, and of a recording medium and an apparatus therefor. Incidentally,the invention is not limited by the embodiments.

Embodiment 1

FIG. 1 is a schematic view representing a recording method by virtue offading florescence on particular phosphors among a plurality of kinds ofphosphors 2 included in a polymer recording thin film 1 (hereinafter,referred to as recording film), in a particular region of the recordingfilm 1.

High density recording is performed on a recording medium 4 formed, on asubstrate 3, with the recording film 1 having the plurality of kinds ofphosphors 2 by using an optical probe 5 formed with a microscopicaperture 50 having a diameter of the wavelength of light or shorter. Theoptical probe 5 is coated with aluminum as a shading film 6 in areasexcept for the microscopic aperture 50. The optical probe 5 is providedwith a wavelength select filter 7 on its light incident side so thatonly selected light out of the light 8 from a light source is incidenton the optical probe 5.

The distance between the optical probe 5 at the microscopic aperture 50of the optical probe 5 and the recording film 1 is controlled to be aconstant value equal to or less than the wavelength of light. Forexample, a laser light is illuminated to the vertically-vibratingoptical probe 5 to detect a change an amplitude by an optical levermethod used in the atomic force microscope (AFM). The change inamplitude is read out as a distance change amount between the opticalprobe 5 and the recording medium 1 and the amplitude change ismaintained constant whereby the distance between the optical probe 5 andthe recording film 1 can be controlled to a constant value equal to orless than the wavelength of light.

As a result of this, near-field light 51 is emitted through themicroscopic aperture 50 and illuminated onto the recording film 1. Thesize (spot size) of illumination on the recording film 1 b thisnear-field light 51 is nearly equal to the size of the microscopicaperture 50. That is, by using the near-field light 51, it is possibleto illuminate only a microscopic region on the recording film 1.

There is a photo-bleaching method used as a method for fadingfluorescence of particular phosphors. In this method, light having acorresponding wavelength to the particular phosphor is illuminatedwhereby the particular phosphor is photooxidized and its fluorescencefades. Photooxidation is used to illuminate light in the presence ofoxygen to change a molecular structure. Hereinafter, the light selectedby the wavelength select filter 7 to fade fluorescence of the phosphors2 is referred to as fading light 9. For example, consideration is madeof a case in which three kinds of phosphors A, B, C are contained in athin film. It is assumed that the center wavelengths of fading light 9corresponding to the phosphors A, B and C are X1, X2 and X3. In the caseof fading fluorescence of the phosphor B, fading light 9 with a centerwavelength X2 is incident on the optical probe 5. This fading light 9has no effect upon fluorescence of the other phosphors A, C.

Consequently, consideration is made of a case that the near-field light51 emitted through the microscopic aperture 50 of the optical probe 5illuminates the recording film 1. It is assumed as a region 10 that thisselected fading light 9 illuminates the recording film 1. The region 10is equal to the size of the microscopic aperture. If fading light 9 withthe center wavelength A2 is incident on the optical probe 5,fluorescence of the phosphor B in the region 10 fades. B* in the figurerepresents that the fluorescence of phosphor B is faded out. Similarly,it is possible in a region 11 to fade fluorescence on the phosphors A, Cby making incident wavelengths λ1, λ2 of fading light 9 on the opticalprobe 5 separately or simultaneously. A*, C* represent that thephosphors A, C have been faded out in fluorescence. The illuminatedregion 11 is equal in diameter to the size of the microscopic aperture.

By the above, the use of near field light through the microscopicaperture makes it possible to reduce one recording bit size as comparedto the conventional optical system using a lens, thus enabling higherdensity recording than the conventional methods. Also, the conventionalmethods have been based on recording with two values of 0, 1 withrespect to one recording bit. However, only one or more particularphosphors among a plurality of different kinds of phosphors are faded influorescence to record on the presence or absence of fluorescence sothat the information amount of one recording bit can be multi-valued tomake possible higher density recording than in the conventional methods.

Embodiment 2

FIG. 2 is a figure representing a reproducing method in which excitationlight is illuminated to the recording medium shown in Embodiment 1 toreceive fluorescent light.

A recording film 1 in its microscopic region is recorded withinformation depending on the presence or absence of fluorescence onphosphors 2, as was shown in Embodiment 1. An optical probe 5 iscontrolled similarly to Embodiment 1. The incidence of excitation light12 provides near-field light 51 through a microscopic aperture 50,making possible illumination only to a microscopic region on therecording film 1. A prism 14 is provided to separate, by wavelength,fluorescent light 13 from the recording film 1. The fluorescent light 13thus separated is received by a detector array 16 having detectors 15corresponding to wavelengths.

Consideration is made of a case in which three phosphors A, B, C existin the recording film 1, as was shown in Embodiment 1. In a region 10two phosphors A, C are left by the recording method of Embodiment 1.From a light source, excitation light 12 capable of exciting all thephosphors A, B, C is incident on the optical probe 5.

If near-field light 51 is illuminated to a region 10, fluorescent light13 is obtained only from the phosphors A, C. The fluorescent light fromthe phosphors A, C is incident on a prism 14 to be separated on awavelength basis. The separated fluorescent light is received by thedetector array 16 having the corresponding detectors 15 to separatedwavelengths. The presence or absence of light reception on each detector15 is put in correspondence to signals 1, 0. If representing thepresence or absence of signals in the order of A, B and C, theflorescent light from the region 10 is given as 1, 0, 1. Similarly, ifexcitation light 12 is illuminated to a region 11, signals 0, 1, 0 areobtained because fluorescence is left only on the phosphor B.

From the above, where the three phosphors are contained, in therecording shown in Embodiment 1 an arbitrary phosphor can be changed influorescence. In the reproduction shown in the present embodiment,multi-valuing to 2 combinations is available by detecting the presenceor absence of a fluorescent light spectrum on each phosphor through thecorresponding detector 15. Similarly, where m kinds of phosphors arecontained in the thin film, multi-valuing is possible to 2^(m)combinations.

Due to this, despite the fact that in the conventional art only twovalues 0, 1 have been applied to one recording bit, arbitrary phosphors2 contained in the recording film 1 are changed in fluorescence so thatthe changes are detected as a wavelength spectrum of fluorescent light13 thereby enabling multi-valuing of information amount on one recordingbit. Also, the use of near-field light 51 through a microscopic apertureof an optical probe 5 can provide reproduction of information out of amicroscopic region of a size equal to or less than a wavelength. As aresult, reproduction is possible higher in density than in theconventional art.

Embodiment 3

FIG. 3 is a schematic structural view of an apparatus for recording andreproducing by applying a mechanism of a near field optical microscope.

The apparatus comprises a recording medium 4 for recording information,an optical probe 5 for illuminating the recording medium 4 withnear-field light for recording/reproducing, a light source system 7,23-25, a distance control system 19-22 for controlling the distancebetween the optical probe and recording medium, a prism 14 forseparating florescent light, a detector array 16 having correspondingdetectors 15 for separated wavelengths, a signal processing circuit 17for reading as signals 0, 1 the presence or absence of light receptionin each detector 15 to process information, and a computer 18 forcontrolling the overall apparatus.

The optical probe 5 has a structure as stated in Embodiment 1, which canbe formed by sharpening a tip of an optical fiber and coating around itwith aluminum except for a portion to be formed into a microscopicaperture. The size of the microscopic aperture is, for example, about100 nm in diameter.

The distance control system for controlling the distance between theoptical probe and recording medium comprises a distance measuring means19 for measuring a distance between a tip of the optical probe S and therecording medium 4, a distance control circuit 20 for generating afeedback signal from a distance measured by the distance measuring means19, and a rough movement mechanism 21 and fine movement mechanism 22 forchanging a distance between the tip of the optical probe 5 and therecording medium 4 in response to this feedback signal. The distancemeasuring means 19 can use, for example, an optical lever of the typeused in an AFM. The rough movement mechanism 21 can use, for example, astepping motor and a rack-and-pinion, while the fine movement mechanism22 can use a piezoelectric element.

The recording medium 4 is obtained, for example, by forming on asubstrate 3 one polymer recording thin film 27 containing three kinds ofphosphors 28, as shown in FIG. 4. For example, as a polymer recordingthin film 27 material there are polybinylcarbazole (PVK) andpoly-p-phenylen (PPV). As the phosphors 28 there are1,1,4,4-tetraphenyl-1-3-butadiene (TPD) and coumarin 6, quinacridone,rubrene, etc. The method for applying a polymer recording thin film 27as above includes, for example, a wet technique including a cast filmtechnique, a spin coat technique, and a polymerization by electrolysis,etc. For example, in the case of the spin coat technique, a polymericmaterial and phosphors are mixed in a solvent of chloroform, xylene,etc., and applied onto a substrate 3 by a spinner, thereby obtaining arecording medium 4.

Consideration is made of a case of performing reproduction using theapparatus explained above. A recording medium 4 is placed on the finemovement mechanism 22. First, the optical probe 5 and the recordingmedium 4 are further apart than a distance at which an interatomic forceis to act on. If the recording medium 4 is approached to the opticalprobe 5 by the rough movement mechanism 21, an interatomic force beginsto act on between the optical probe 5 and the recording medium 4. Atthat time, the rough movement mechanism 21 is halted. Then, therecording medium 4 is raised or lowered by the fine movement mechanism22, wherein the fine movement mechanism 22 is controlled so as to give apredetermined interatomic force. Because the interatomic force acts onseveral tens nanometers or less, the distance between the optical probe5 and the recording medium 4 can be controlled to be fully smaller thana wavelength of a visible portion or ultraviolet portion of light and tobe a constant value.

A reproducing light source 23 uses, for example, a semiconductor laserso that the light from the reproducing light source 23 is focused by alens 25 and incident on an optical probe 5 incident end. As a result,near-field light is given off through a microscopic aperture at anoptical probe 5 tip, illuminating a microscopic region on the recordingmedium 4. For example, the microscopic region has a size ofapproximately 100 nm that is almost equal to a diameter of themicroscopic aperture. By the near-field light illuminated onto therecording medium 4 from the optical probe 5, the phosphors keeping influorescence are excited to generate fluorescent light. The fluorescentlight is separated by a prism 14.

The separated fluorescent light is received by a detector array 16having corresponding detectors 15 for the separated wavelengths. Thepresence or absence of light reception on each detector 15 is fed to asignal processing circuit 17 to process signals 1, 0. The processedsignal is fetched by a computer 18 to reproduce information.

For recording, means to control a distance between the optical probe 5and the recording medium 4 to be a constant value is similar toreproduction. The light from the recording light source 24 is giventhrough the wavelength select filter 7 to the lens 25 to be focused, andincident on an incident end of the optical probe 5. By the wavelengthselect filter 7, only light having a corresponding wavelength toparticular phosphors is incident on the optical probe 5. The recordinglight source 24 can use, for example, an ultraviolet ray lamp. The lightincident on the optical probe 5 is emitted through an aperture at thetip of the optical probe 5 and illuminates a microscopic region on therecording medium 4, fading out fluorescence of particular phosphors. Thesize of the microscopic aperture is, for example, approximately 100 nm,similarly to that upon reproduction.

When recording/reproducing was performed on the recording medium 4having the three kinds of phosphors 28 shown in FIG. 4 by the abovemethod, 2³ combinations of signals could be recorded and reproduced.Also, each bit size was approximately 100 nm thus realizing a bit sizeof a using wavelength or smaller.

In this manner, it is possible to obtain a recording medium 4 for highdensity recording/reproducing by mixing a plurality kinds of phosphors28 in one-layered polymeric recording thin film 27 and applying it ontoa substrate 3. The recording medium 4 can be manufactured at low pricebecause of manufacture by a wet method.

Meanwhile, a near-field optical microscope mechanism was applied toilluminate near-field light emitted through the microscopic aperture ofthe optical probe 5 tip onto this recording medium. By doing so, it ispossible to illuminate only a microscopic region on the recording medium4. Furthermore, for this microscopic region fluorescence of arbitraryphosphors were faded to thereby perform multi-value recording so thatthe information recorded in multi-values could be read out offluorescent spectrums.

From the above, it is possible to obtain a recording/reproducingapparatus higher in density than the conventional apparatus by reductionin recording bit size and multi-valuing information of each recordingbit.

Embodiment 4

FIG. 5 is a schematic view representing a recording medium 40 formedwith polymeric recording thin films 30 in a corresponding number oflayers to the kinds of phosphors 31 wherein each polymeric recordingthin film 30 has only one kind of phosphor 31.

As a preparing method, a polymeric material and one kind of phosphor aremixed in a solvent and applied onto a substrate 3 using a wet technique.The solvent, polymeric material, phosphors 31, substrate 3, etc. may bethose as exemplified in Embodiment 3. Due to this, one layer ofpolymeric recording thin film 30 is formed. A polymeric recording thinfilm 30 is formed thereon by using another one of phosphors 31 in asimilar manner. By repeating this, a recording medium 40 comprising aplurality of phosphors can be made. It is preferred as a layering orderto form a shorter wavelength one of the phosphors on a substrate sidebecause the fluorescent light from phosphors on the substrate side isnot absorbed by the phosphors layered over that.

As shown in FIG. 4, where a plurality of kinds of phosphors 28 areformed in the same polymeric thin film 27, if excitation light isilluminated, energy transfer occurs to the phosphors that are readier tobe excited among the different kinds of phosphors. Energy transferoccurs when an electron excited in one molecule and a hole in a groundstate turns into a dipole so that the dipole moves between adjacentmolecules. In a phosphor 31 not ready to be excited, excitation energyis reduced and fluorescence intensity is lowered with a result thatthere may be a case wherein fluorescent intensity differ between thephosphors.

However, in the present embodiment, because the different kinds ofphosphors are isolated, energy transfer is suppressed between thedifferent kinds of phosphors. Thus, fluorescent light can be efficientlyobtained from-each phosphor.

From the above, by dividing the different phosphors in the separatelayers, a recording medium 40 could be obtained that is suited for highdensity recording/reproducing with higher fluorescent efficiency thanthat of the recording medium 4 shown in Embodiment 3.

Embodiment 5

FIG. 6 is a schematic view representing a recording medium 41 formedwith inorganic insulation films 32 between the layered polymericrecording thin films 30 shown in FIG. 5. As a preparing method, apolymeric recording thin film 30 containing one kind of phosphors 31 isapplied onto a substrate 3 by a wet method. Thereon, an inorganicinsulation film 32 is formed. Here, the inorganic insulation film 32 isa transparent one having such a wide energy gap as not to absorbnear-field light or fluorescent light. For example, when film-formingsilicon nitride by sputtering, a transparent film is obtained byproperly setting a gas flow rate, nitrogen ratio, etc. Furthermore, byforming layers in order using another one of phosphors in a similar way,a recording medium 41 can be manufactured.

Due to this, because the insulation film 32 has a high energy gap ascompared to the phosphors 31, energy transfer occurs less in a polymericthin film 32 interface having a different kind of phosphors 31 than inthe case of Embodiment 4. That is, because energy transfer occurs onlybetween the same kind of phosphors 31, excitation efficiency becomeshigh and fluorescent efficiency increases. As a result, higher intensityfluorescent light is obtained than that in Embodiment 4, and the S/Nratio upon reproduction is increased.

From the above, by forming the insulation films 32 between the polymericthin films 30 having each of phosphors 31, a recording medium 41 suitedfor high density recording/reproducing could be obtained which isimproved in S/N ratio as compared to the recording medium 40 ofEmbodiment 4.

Embodiment 6

FIG. 7 shows a schematic view representing a recording medium 4 formedwith a metal film 33 between a lowermost polymeric recording thin film27 or 30 and a substrate 3, in the recording medium 4, 40, 41 ofEmbodiments 3 to 5. A metal film 33 is formed on a substrate 3. As themetal film 33, there is for example aluminum or chromium. In the case ofaluminum, a film is formed by sputtering or resistance-heating.Thereafter, polymeric recording thin films 27 or 30 containing phosphors31 are formed or layered in a similar manner to the way shown inEmbodiments 3 to 5.

Due to this, the excitation light illuminated on a recording mediumsurface transmits through each of the polymeric recording thin films 27or 30, and then reflected upon the metal film 33 and illuminates againthe polymeric thin films 27 or 30.

As a consequence, excitation efficiency is improved as compared toEmbodiments 3 to 5, increasing fluorescent intensity. From the above, byforming the metal film between the lowermost polymeric recording thinfilm 27 or 30 and the substrate 3, it is possible to obtain a recordingmedium further suited for high density recording/reproducing.

Embodiment 7

FIG. 8 is a schematic view representing a recording method to fadefluorescence of the phosphors, at a particular region of the recordingfilm 1, in the order readier to be photooxidized by fading light, amonga plurality of phosphors contained in the recording film 1.

In order to fade fluorescence in the order of a phosphor readier to bephotooxidized, varied is an illumination integrated light amount(hereinafter referred to as illumination amount) of fading light.Illumination amount is a product of illumination light intensity(hereinafter referred to as light intensity) and time. Also, the light 8from the light source is directly given as fading light, differentlyfrom Embodiment 1.

Consideration is made of a case in which a polymeric recording film 1contains three kinds of phosphors D, E, F. The order of a phosphorreadier to be photooxidized is given D, E, F. That is, the illuminationamount if increased causes photooxidation in the order of from D to F infading fluorescence. It is assumed that D, E and F are respectively, forexample, rubrene, oxadiazole derivative (PBD) and tetraphenylbutadiene(TPB). The light source for fading light 8 uses a mercury lamp. When theillumination amount is varied, fluorescence fades out in the order ofrubrene, PBD and TPB.

Similarly to Embodiment 1, the microscopic aperture 50 with a size of awavelength or smaller formed in the optical probe 5 is approached to therecording film 1 to a distance of the wavelength or shorter. Thenear-field light illumination region at this time is in almost the samesize as the diameter of the microscopic aperture. The region illuminatedby near-field light 51 is taken as a region 34. In the region 34, theillumination amount for fading fluorescence of the phosphor D is smallerthan a threshold of an illumination amount for fading fluorescence ofthe phosphors E, F but greater than a threshold of the phosphor D.Similarly, in a region 35 the illumination amount for fadingfluorescence of the phosphors D, E is smaller than a threshold of anillumination amount for fading fluorescence of the phosphor F butgreater than a threshold of the phosphors D, E.

By controlling the illumination amount using near-field light 51, it ispossible in the microscopic region to fade fluorescence of the threekinds of phosphors 36 in the order of a phosphor readier to bephotooxidized, i.e. in the order of D, E and F. Consequently,multi-value recording for each bit is rendered feasible by the presenceor absence of fluorescence on the phosphor, similarly to Embodiment 1.Note that, for the case of three kinds of phosphors, multi-valuing ispossible in three combinations. Similarly, m combinations ofmulti-valuing is possible for m kinds of phosphors. Also, by usingnear-field light 51 through the microscopic aperture 50, each bit sizecan be made smaller than that of a case using the conventional opticalsystem.

In Embodiment 1 the wavelength of a fading light for fading fluorescenceis determined corresponding to a phosphor. If the corresponding fadinglight wavelengths to two different phosphors are the same, it isimpossible to fade only the florescence of one phosphor. As compared tothis, because the method of varying the illumination amount of thepresent embodiment is not dependent upon a wavelength, this point can beavoided thus making possible multi-value recording even in a case ofcontaining in the recording film 1 the phosphors that are same in fadinglight wavelength.

Meanwhile, in Embodiment 1, the apparatus is complicated because ofusing a wavelength select filter and requires to vary the fading lightwavelength in accordance with a phosphor on a recording-bit basis thuscomplicating the recording method. In the method of varying theillumination amount as in the present embodiment, it is satisfactoryonly to vary the illumination amount on the recording-bit basis withoutrequiring a wavelength select filter. Accordingly, it is easy to realizemulti-valued high density recording.

From the above, the use of a near-field light through a microscopicaperture can reduce one recording bit size as compared to theconventional optical system using a lens, enabling higher densityrecording than the conventional. Also, although in the conventionalrecording has been by binary values of 0, 1 for one recording bit,fluorescence of a plurality of kinds of phosphors contained in the thinfilm is faded in the order of a phosphor readier to be photooxidized dueto fading light, whereby the information amount of one recording bit canbe rendered multi-valued enabling higher density recording than theconventional.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, the use ofnear-field light can reduce the size of one recording bit as compared tothe conventional optical system using a lens, thus enabling higherdensity recording than the conventional system. Also, although theconventional system uses recording of binary values of 0, 1 for onerecording bit, among a plurality of kinds of phosphors only oneparticular kind of phosphor is faded in fluorescence to record thepresence or absence of fluorescence, rendering the information amount ofone recording bit multi-valued and enabling higher density recordingthan the conventional system.

Also, according to the present invention, the use of near-field lightcan reduce the size of one recording bit as compared to the conventionaloptical system using a lens, thus enabling higher density recording thanin the conventional system. Also, although the conventional methodinvolves recording of binary values of 0, 1 for one recording bit, anear-field light having a corresponding wavelength to a particularphosphor among a plurality of kinds of phosphors is illuminated to fadefluorescence of the particular phosphor and record the presence orabsence of fluorescence, thereby rendering the information amount of onerecording bit multi-valued and enabling higher density recording than inthe conventional method.

Also, according to the present invention, the use of near-field lightcan reduce the size of one recording bit as compared to the conventionaloptical system using a lens, thus enabling higher density recording thanthe conventional system. Also, when two kinds of phosphors are the samein light wavelength for fading fluorescence, it is impossible to varythe wavelength to fade fluorescence of either one of them. However,because the method of changing the illumination amount is not dependentupon the wavelength, this point can be avoided. Even where usingphosphors having the same light wavelength to fade fluorescence, onephosphor can be faded in fluorescence. Also, because the method ofchanging the illumination amount does not require a wavelength selectfilter, the apparatus can be simplified and the cost can be reduced.

Also, according to the present invention, although in the conventionalmethod the information has been binary values of 0, 1 for one recordingbit, an arbitrary phosphor contained in the recording film is changed influorescence and the change is detected as a wavelength spectrum of thefluorescent light, enabling reproduction of multi-valued information.Also, the use of a near-field light could reproduce information from amicroscopic region. As a result, information recorded with higherdensity then that of the conventional system is possible to reproduce.

Also, according to the present invention, a recording medium is usedwhich is characterized by forming thin films having at least one or moretypes of phosphors on a substrate, thereby obtaining a recording mediumfor high density optical recording/reproducing. Furthermore, because therecording medium can be manufactured by a wet scheme, manufacture ispossible at low price.

Also, according, to the present invention, because phosphors areisolated, energy transfer between different phosphors is suppressed. Itis possible to obtain a recording medium for high density opticalrecording/reproducing which can obtain fluorescent light from eachphosphor effectively.

Also, according to the present invention, energy transfer is caused onlybetween the phosphors to thereby increase excitation efficiency,increasing fluorescent efficiency and obtaining intense fluorescentlight. It is possible to obtain a recording medium for high densityoptical recording/reproducing in which the S/N ratio increases duringreproduction.

Also, according to the present invention, the excitation lightilluminated to a recording medium surface transmits through each thinfilm, and reflects on the metal film and again illuminates the thinfilm, improving excitation efficiency. Thus, a recording medium for highdensity optical recording/reproducing can be obtained in whichfluorescent light intensity increases.

Also, according to the present invention, only a microscopic region ofthe recording medium can be illuminated by a near-field light. Using thenear-field light, it is possible to fade fluorescence of the phosphorscontained in the microscopic region of the recording medium, obtaining ahigh density optical recording apparatus.

Also, according to the present invention, a high density opticalreproducing apparatus can be obtained which illuminates a near-fieldlight to a recording medium having one or more types of phosphors andmicroscopically faded in particular fluorescence of the phosphors tospecify a fluorescent phosphor from an obtained spectrum.

What is claimed is:
 1. An optical recording method, comprising the stepsof: providing a recording medium having therein a plurality of differenttypes of phosphors each being arranged at each of a plurality ofmicroscopic regions, each of the different types of phosphors having afluorescence characteristic that is altered in response to irradiationwith near-field light having a predetermined wavelength so that thefluorescent characteristic of the phosphors may take on one of twodifferent states; and successively irradiating microscopic regions ofthe recording medium with a near-field light having a wavelength set toselectively alter the fluorescence characteristic of selected ones ofthe phosphors in the irradiated microscopic regions of the recordingmedium to represent a given data state in accordance with data to bestored.
 2. An optical recording method according to claim 1; wherein therecording medium comprises a support substrate, and one or more thinfilms formed on the support substrate and containing the phosphors inregularly arranged microscopic regions.
 3. An optical recording method,comprising the steps of: providing a recording medium having therein aplurality of different types of phosphors each being arranged at each ofa plurality of microscopic regions, each of the different types ofphosphors having a fluorescence that is faded in response to irradiationwith near-field light having a predetermined wavelength so that thefluorescence of the phosphors may take on one of two different states;and successively irradiating microscopic regions of the recording mediumwith a near-field light having a wavelength set to selectively fade thefluorescence of selected ones of the phosphors in the irradiatedmicroscopic regions of the recording medium to represent a given datastate in accordance with data to be stored.
 4. An optical recordingmethod, comprising the steps of: providing a recording medium havingtherein a plurality of different types of phosphors each being arrangedat each of a plurality of microscopic regions, each of the differenttypes of phosphors having a fluorescence characteristic that is alteredin response to irradiation with a predetermined amount of near-fieldlight so that the fluorescence characteristic of the phosphors may takeon one of two different states; and selectively irradiating microscopicregions of the recording medium with a near-field light of an amounteffective to alter the fluorescence characteristic of selected ones ofthe phosphors in the irradiated microscopic regions of the recordingmedium to represent a given data state in accordance with data to bestored.
 5. An optical recording method according to claim 4; wherein therecording medium comprises a support substrate, and one or more thinfilms formed on the support substrate and containing the phosphors inregularly arranged microscopic regions.
 6. An optical reproducing methodcomprising the steps of: providing a recording medium according to claim5; irradiating a microscopic region of the recording medium with anear-field light to produce reflected light having a given spectrum; anddetermining a state of data stored in the irradiated microscopic regionby determining fluorescent characteristics of one or more of thephosphors based on the spectrum of reflected light.
 7. A recordingmedium comprising: a support substrate; and a thin film containing aplurality of different types of phosphors formed on the supportsubstrate in each of a plurality of microscopic regions, each of thedifferent types of phosphors having a fluorescent characteristic that isaltered in response to irradiation with near-field light having one of apredetermined wavelength or intensity so that irradiation of arespective phosphor in a microscopic region with near-field light mayalter the fluorescence characteristic of the respective phosphor torepresent a given data state.
 8. A recording medium according to claim7; wherein the wavelength or intensity of light which alters thefluorescence characteristic of the phosphors is different for eachdifferent type of phosphor.
 9. A recording medium according to claim 8;further comprising a reflective layer formed between the supportsubstrate and the thin film so that incident light that has beentransmitted through the thin film is reflected by the reflective layerand re-transmitted through the thin film to increase fluorescentintensity of the phosphors.
 10. A recording medium according to claim 8;wherein the thin film comprises a polymer.
 11. A recording mediumaccording to claim 10; wherein the polymer comprises at least one ofpolybinylcarbazole (PVK) and poly-p-phenylen (PPV).
 12. A recordingmedium according to claim 8; wherein the phosphors are selected from thegroup consisting of 1,1,4,4-tetraphenyl-1-3-butadiene (TPD), coumarin 6,quinacridone and rubrene.
 13. A recording medium comprising: a supportsubstrate; and a plurality of thin films each having therein only onetype of phosphor formed on the support substrate, the respective thinfilms each having a different type of phosphor from the others, thephosphors having a fluorescent characteristic that is altered inresponse to irradiation with near-field light having at least one of agiven wavelength and a given amount.
 14. A recording medium according toclaim 13; further comprising an insulation film disposed betweenadjacent thin films formed on the support substrate.
 15. A recordingmedium according to claim 13; wherein each thin film contains only oneof the plural types of phosphors in each of a plurality of microscopicregions, each of the plural types of different phosphors having afluorescence characteristic that is altered in response to irradiationwith near-field light having one of a predetermined wavelength andintensity, which is different for each of the different types ofphosphors.
 16. A recording medium according to any one of claims 7 to14; further comprising a metal film formed on the support substratebetween the support substrate and the thin films so that the metal filmunderlies the plural thin films.
 17. An optical recording apparatuscomprising: a recording medium having therein one or more phosphors ineach of a plurality of microscopic regions, the one or more phosphorseach having a fluorescence characteristic that is altered in response toirradiation with near-field light having one of a predeterminedwavelength or a predetermined amount so that the fluorescencecharacteristic of the phosphors may take on one of two different states;a recording head for producing the near-field light to irradiate therecording medium; an adjusting mechanism for adjusting at least one of awavelength and an amount of the near-field light; and an approachingmechanism to cause the recording medium and the recording head toapproach one another and come into close proximity.
 18. An opticalreproducing apparatus, comprising: a recording medium having therein aplurality of different types of phosphors each being arranged at each ofa plurality of microscopic regions, each of the different types ofphosphors having a fluorescence characteristic that is altered inresponse to irradiation with near-field light having one of apredetermined wavelength or a predetermined amount so that thefluorescence characteristic of the phosphors may take on one of twodifferent states; a reading head for irradiating the near-field lightonto the recording medium to excite the phosphors to produce reflectedlight having a fluorescent component; means for specifying selectedfluorescent ones of the phosphors based on the fluorescent component ofthe reflected light; and an approaching mechanism to cause the recordingmedium and the recording head to approach one another and come intoclose proximity.
 19. An optical recording medium comprising: a supportsubstrate; a plurality of regularly arranged microscopic regions in thesupport substrate; and one or more different types of fluorescentmaterials disposed in each of the microscopic regions, each respectivetype of fluorescent material being responsive to light having adifferent predetermined wavelength to fade the fluorescence thereof sothat irradiation of the fluorescent materials of selected microscopicregions with a near-field light at the predetermined wavelength fadesthe fluorescence of desired fluorescent materials in accordance withdata to be stored such that the fluorescent characteristic of theirradiated phosphors represents the stored data.
 20. An opticalrecording medium according to claim 19; wherein the fluorescentmaterials comprise phosphors.
 21. An optical recording medium accordingto claim 19; wherein the phosphors are photooxidized by light having thecorresponding predetermined wavelength so that the fluorescence thereofis faded.
 22. An optical recording medium according to claim 19; whereina plurality of the different types of fluorescent materials are arrangedat each of the plurality of successive microscopic regions of therecording medium so that each microscopic region of the recording mediumcan be used to store a plurality of bits of data.
 23. An opticalrecording medium according to claim 19; wherein the recording mediumcomprises a support substrate and one or more thin film layerscontaining the one or more different types of fluorescent materialsformed on the support substrate.
 24. An optical recording mediumaccording to claim 23; wherein the recording medium further comprises areflective layer disposed between the support substrate and the one ormore thin film layers so that incident near-field light that has beentransmitted through the one or more fluorescent materials is reflectedby the reflective layer and re-transmitted through the fluorescentmaterials to increase fluorescent intensity.
 25. An optical recordingmedium according to claim 23; wherein the one or more thin film layersare formed of a polymer.
 26. An optical recording medium according toclaim 25; wherein the polymer comprises at least one ofpolybinylcarbazole (PVK) and ply-p-phenylen (PPV).
 27. An opticalrecording medium according to claim 19; wherein the recording mediumcomprises a support substrate and a plurality of thin films formed onthe support substrate, each thin film containing a different type offluorescent material.
 28. An optical recording medium according to claim27; wherein the recording medium further comprises an insulation filmformed between the respective thin films to prevent energy transferbetween the fluorescent materials contained in adjacent thin films. 29.An optical recording medium according to claim 19; wherein the one ormore fluorescent materials are selected from the group consisting of1,1,4,4-tetraphenyl-1-3-butadiene (TPD), coumarin 6, quinacridone andrubrene.
 30. A method of fabricating an optical recording medium,comprising the steps of: providing a support substrate; and forming athin film layer on the support substrate, the thin film layer havingdisposed therein a plurality of different types of fluorescent materialsat each of a plurality of regularly arranged microscopic regions, eachtype of fluorescent material having a fluorescent characteristic that isaltered at a different predetermined wavelength of near-field light sothat irradiation of fluorescent materials of selected microscopicregions with near-field light at a given wavelength alters thefluorescence characteristic of only one of the fluorescent materials.31. A method of fabricating an optical recording medium according toclaim 30; wherein the step of forming a thin film layer on the supportsubstrate comprises a wet film forming technique selected from the groupconsisting of a cast film technique, a spin coat technique, andpolymerization by electrolysis.
 32. A method of fabricating an opticalrecording medium according to claim 31; wherein the step of forming thethin film layer on the support substrate further comprises the steps ofmixing a polymer with the one or more fluorescent materials and applyingone or more thin films of the mixture to the supporting substrate.
 33. Amethod of fabricating an optical recording medium according to claim 30;wherein the step of forming the thin film layer on the support substratecomprises the steps of mixing a polymer with each of the one or morefluorescent materials to produce a mixture for each of the one or moredifferent types of fluorescent materials, and applying a thin film ofeach of the mixtures to the support substrate such that each of thedifferent types of fluorescent materials is arranged at each of themicroscopic regions and each microscopic region can be used to storemulti-bit data.
 34. A method of fabricating an optical recording mediumaccording to claim 33; further comprising the step of forming aninsulation film between respective thin films to prevent energy transferbetween fluorescent materials of different thin films.
 35. A method offabricating an optical recording medium according to claim 30; furthercomprising the step of forming a reflective thin film layer between thesupport substrate and the thin film layer so that incident near-fieldlight that has been transmitted through the one or more fluorescentmaterials is reflected by the reflective thin film layer andre-transmitted through the fluorescent materials to increase fluorescentintensity.
 36. A method of fabricating an optical recording mediumaccording to claim 30; wherein the thin film layer comprises a polymerhaving the one or more fluorescent materials dispersed therein.
 37. Amethod of fabricating an optical recording medium according to claim 36;wherein the polymer comprises at least one of polybinylcarbazole (PVK)and poly-p-phenylen (PPV).
 38. A method of fabricating an opticalrecording medium according to claim 30; wherein the one or morefluorescent materials are selected from the group consisting of1,1,4,4-tetraphenyl-1-3-butadiene (TPD), coumarin 6, quinacridone andrubrene.